fix: attempt to fix windows issues with example code snippets (reactjs#1385)

This PR may (!?) fix the issue with windows support the GraphQL query
not running. Will need to be validated by someone on Windows, but this
_seems_ like it'll work.

Author: DSchau

plugins/gatsby-transformer-home-example-code/gatsby-node.js

@@ -1,4 +1,5 @@
-const crypto = require(`crypto`);
+const crypto = require('crypto');
+const path = require('path');
 
 const createContentDigest = obj =>
   crypto
@@ -14,7 +15,7 @@ exports.onCreateNode = async ({actions, node, loadNodeContent}) => {
 
   if (
     sourceInstanceName === 'content' &&
-    relativeDirectory === 'home/examples' &&
+    relativeDirectory === path.join('home', 'examples') &&
     ext === '.js'
   ) {
     const code = await loadNodeContent(node);